As is known in the art, in power electronics there exists a class of circuits referred to as power converter circuits (or more simply “power converters”). Power converters convert electrical energy from one form to another (e.g. converting between ac and dc, changing the voltage or frequency of a signal or some combination of the above).
As is also known, power supplies may include power converters used for direct current (dc) distribution systems, computers, telecommunications and data centers, as well as for transportation, lighting, displays, and medical applications among many other areas require high power density and fast response characteristics. Ideally power supplies provide electrical isolation between a source and a load and operate efficiently. In many cases, there is a desire for efficiency at high conversion ratios and/or over wide operating ranges of voltages and/or powers. There is also a desire to provide power supplies having a high degree of integration, manufacturability and reliability. Traditionally, power supplies having magnetic converter-based architectures with isolation transformers are widely used, such as forward converters, flyback converters and related architectures. Such architectures are generally simple, low-cost and easy to control.
There is, however, a continued trend to operate power converters at ever increasing switching frequencies. As switching frequencies increase, the converter timing required in the aforementioned magnetic converter-based architectures becomes difficult to satisfy, and the effects of parasitic circuit elements (or more simply “parasitics”) may significantly increase loss characteristics of the converter.
As is also known, one approach to providing converters in such high frequency applications includes the use of circuits which utilize high-gain transformers or coupled inductors. Circuits incorporating tapped inductors can provide desirable duty ratios and reduce device switching stress. Leakage inductances of such tapped inductors, however, can resonate (or “ring”) with a parasitic capacitance of the switches at certain frequencies. This limits the feasibility of this approach at high switching frequencies.
High-frequency-link architectures can reduce or eliminate this ringing problem by “absorbing” parasitic circuit elements, such as transformer leakage inductance, into circuit operation.
Such circuits can often also be implemented utilizing so-called “soft switching” techniques which enables switching at frequencies which are higher than operational frequencies of conventional hard-switched architectures.
Nevertheless, as desired operating switching frequencies for power converters keep increasing, parasitic effects which are sometimes ignored (such as the proximity effect loss and transformer parasitic capacitances), can become very important. Furthermore, requirements that a system achieve high performance (i.e. the system achieves a desired level of efficiency and power density, in addition to meeting other functional requirements including but not limited to ac line synchronization, total harmonic distortion (THD), and power factor) over a wide operating range, e.g. universal line input voltages, makes system designs even more challenging.